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Area Forecast Discussion (AFD)

Issued by Marquette, MI (MQT)

FXUS63 KMQT 241622

Area Forecast Discussion
National Weather Service Marquette MI
1222 PM EDT Sat Aug 24 2019

.SHORT TERM...(Today and tonight)
Issued at 450 AM EDT SAT AUG 24 2019

WV imagery and RAP analysis indicated a mid/upper level ridge over 
the Upper Mississippi Valley resulting in weak northerly flow 
through the western Great lakes. At the surface, ridging extended 
from James Bay and northern Ontario into the northern Great Lakes. 
Mostly clear skies prevailed across Upper Michigan with some patchy 

Today, as the sfc ridge slowly builds to the east, southerly winds 
will develop but should remain relatively light. This will allow 
prominent lake breezes to develop. Sunshine with mixing to around 4k 
ft will boost temps into the mid 70s inland with readings closer to 
70 along the Great Lakes. The dry air will also remain in place as 
dewpoints remain generally in the upper 40s. 

Tonight, otherwise favorable radiation cooling conditions with PWAT 
values at or below 0.5 inch will be limited by slightly stronger 
southerly flow and boundary layer mixing over the west. Temps should 
still drop into the lower to mid 40s inland but will remain in the 
lower to mid 50s near the Great Lakes.

.LONG TERM...(Sunday through Friday)
Issued at 402 AM EDT SAT AUG 24 2019

An active long-term period but save for one brief period, the fall-
like weather continues. The big area of high pressure that'll be 
overhead today will be exiting to the northeast Sunday morning. At 
the same time, models are in good agreement that a seasonably strong 
jet will be digging into the northwestern U.S., which will be the 
beginning of our next weather-maker Monday and Tuesday. Behind that 
system is another shot of cool air for Wednesday, and then perhaps 
another weaker system Thursday with another chance of rain. Now the 

Sunday looks nice, dry, and mostly sunny with highs in the 70s 
across the board. unlike today, however, it will be breezy as the 
aforementioned high continues to depart and the pressure gradient 
increases ahead of the next trough. With plenty of dry air left 
aloft, however, including 700 mb RH less than 10%, the concern 
Sunday will be for this combination of dry air and gusty winds to 
lead to some fire weather potential. At the moment, it looks like 
winds will be from S or SE, so this should advect higher dew point 
air inland over the east and south-central, especially closest to 
Lake Michigan. Over the interior west, however, was a bit aggressive 
in mixing out the low levels. Right now have Min RH around 30% but 
would not be surprised to see that tick even lower. Most of the area 
has not seen measurable rain since last Sunday, and remains in the 
"abnormally dry" (D0 drought) category, so the fire wx potential 
Sunday will certainly need to be watched.

That changes by late Sunday night, however. In contrast to this 
weekend's drier air, much more moist air will be advecting in over 
the far west late Sunday night and then across the rest of the U.P. 
Monday morning out ahead of a mid-level short wave digging into the 
Northern Plains and then moving into northern Minnesota. The 
question here is just how quickly this moist air moves in Monday, 
and how much of the daylight hours we can salvage. With how very dry 
the antecedent air will be, my inclination is to hedge slower with 
rain arrival. Right now, have chance POPs making to the Keweenaw and 
then down through Baraga and Iron Counties through 18z, and only 
slight chance east of there. 

Eventually, however, strong theta-e advection will win out and it 
will rain, with likely to categorical POPs moving across the U.P. 
from 18z Monday to 12z Tuesday. Scaled back what the NBM was giving, 
but still ended up with three quarters of an inch to a little over 
an inch of rain for everyone. PWATs are high enough (1.6"+) and 
forcing is strong enough to realize these amounts. Main negating 
feature will be the lack of much/any elevated CAPE (except for the 
NAM. of course...). If some training cells set up, could be a low-
end hydro threat, but again, seeing as we're running drier than 
normal, not really too worried about that at this time. Could also 
be a rumble or two of thunder, especially if the NAM's elevated CAPE 
comes to fruition, but this is not a setup for any sort of 
strong/severe/widespread thunderstorms; the focus should remain on 
the potential for moderate to heavy rain.

The system's cold front pushes through early Tuesday and then the 
CAA begins. With the main upper level low remaining in place through 
Wednesday, that means a couple cool, cloudy, and breezy days. The 
core of the cool air mass could have 850 mb temps as low as ~3-4 C 
which, overtop Lake Superior with skin temps in the 60s F (or upper 
teens C), means lake-effect rain showers will be possible Wednesday 
for the west wind belts. Some of the models are 
also hinting at our first Lake Superior gale of the season 
Wednesday, but for now have capped gusts at 32 knots and will 
continue to monitor as we get closer. This morning's models want to 
bring in another wave with shower chances Thursday. At the 
moment next weekend looks dry.

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1222 PM EDT SAT AUG 24 2019

VFR conditions are expected through the forecast period.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 450 AM EDT SAT AUG 24 2019

The wind will remain at or below 20 knots through Sunday and then 
increase to 15 to 25 knots Sun night into Monday. South winds are 
expected to 30 knots with a few gale force gusts to 35 knots across 
the extreme eastern part of Lake Superior late Monday. Winds then 
are 20 to 30 knots across all of Lake Superior on Tue through Wed 
with a cold front moving through the area. Tue through Wed would be 
the strongest wind for the forecast period with a few gale force 
gusts possible at times.

Upper Michigan...
Lake Superior...
Lake Michigan...